Field of the Invention
The present invention relates to a multilayer circuit substrate formed by alternately stacking insulating layers and conductive layers, and particularly relates to a high frequency signal transmission technology.
Description of Related Art
It is well-known that technology such as strip lines, microstrip lines, and coplanar lines are used for high frequency signal transmission technology in multilayer circuit substrates having high frequency circuits. When two transmission lines intersect in such a multilayer circuit substrate, signal lines are formed in different conductive layers at least at each intersection area of these signal lines, which correspond to the center conductor of each transmission line. A structure is disclosed in Patent Document 1 in which two microstrip line structures are combined together in a simple manner. In this structure, a ground conductor of the first microstrip line is placed between a signal line of the first microstrip line and a signal line of the second microstrip line. In Patent Document 2, a structure is disclosed in which the signal lines of the first and second microstrip lines are each formed on the surface of the multilayer circuit substrate, and the ground conductor is formed on the bottom of the multilayer circuit substrate. In other words, the first and second microstrip lines use a common ground conductor. At the intersection area of these microstrip lines, the signal line of the first microstrip line is formed inside the multilayer circuit substrate, and both ends of the signal line are connected to a signal line on the surface layer via a through-hole.